The present invention relates to a novel photopolymerizable composition having excellent properties for use as a solder resist in production of printed circuit boards or as an electroless plating resist and therefore suited for use in preparation of a permanent protective mask. More particularly, the present invention relates to a photopolymerizable composition suited for use as a contact exposure type solder photoresist for printed circuit boards on which the resist is applied and, after removing the solvent, image exposure and development are conducted to form a desired pattern.
Screen printing method has been popularly used for forming a solder resist used in the production of printed circuit boards. This method, however, had the problem in resolving performance and improvement thereof has been desired.
As a resist forming technique by which excellent resolving performance is provided, there is known a method in which a liquid photosensitive composition is applied on the whole surface of a circuit-formed base plate and, after removing the solvent by heating, image exposure is made through a mask, followed by the development to form a resist patern. However, this method also had the disadvantages such as possible adhesion of the mask to the surface coat of the base plate during the exposure due to high tackiness of the coat after removal of the solvent, poor developing performance, sensitivity and solvent resistance, and unsatisfactory adherence to the solder circuit.
Screen ink compositions for solder resist containing a compound such as trisacryloyloxyethyl isocyanurate represented by the following formula (I) and an oligomer or monomer having a molecular weight of not more than 5,000 have been known (Japanese Patent Application Laid-Open (KOKAI) Nos. 25371/83 and 51962/84): ##STR3## (wherein R.sup.1, R.sup.2 and R.sup.3 represent hydrogen atom, ##STR4## and two or more of them are not hydrogen atom at the same time).
The coating film formed from these compositions has tackiness, but since these compositions are intended to be used as screen ink for forming images by printing and no step of image exposure through a mask is involved, the surface tackiness poses no problem. However, in the case of the resist forming method of the present invention wherein image exposure is made through a mask, the surface tackiness becomes a serious problem. Also, in the case of screen ink, sensitivity at the time of image exposure and developing performance offer no problem since no step of image exposure and development is involved, but they become a problem in the case of the resist forming method of the present invention.
As a result of the studies for solving the problems, it has been found that a composition containing at least (A) a high-molecular compound with a weight-average molecular weight of not less than 10,000 having a polymerizable double bond in the side chain and (B) a polymerizable monomer represented by the following formula (I), in the case of having formed a coating film after removing the solvent, the thus obtained coating film showing small in tackiness, good developability, high sensitivity, solvent resistance and excellent adhesiveness to solder, and the present invention has been attained on the basis of this finding. ##STR5## (wherein R.sup.1 to R.sup.3 represent hydrogen atom, ##STR6## and two or more of them are not hydrogen atom at the same time).
The object of the present invention is to provide a coating solvent-removing type photosensitive resist composition containing a specific high-molecular compound, in which in the case of having formed a coating film after removing the solvent, the thus obtained coating film shows small in tackiness, high in sensitivity at the time of image exposure through a mask and excellent in developability.